Design for an air distribution unit



FIG. 1 is a front and left side perspective view of an air distribution unit showing my new design;

FIG. 2 is an enlarged front elevation view thereof;

FIG. 3 is an enlarged top plan view thereof;

FIG. 4 is an enlarged left side elevation view thereof, the opposite side being a mirror image of that shown;

FIG. 5 is an enlarged rear elevation view thereof; and

FIG. 6 is an enlarged bottom plan view thereof. 

The ornamental design for an air distribution unit, as shown and described. 